As conventional optical information recording medium, for example, rewritable optical discs such as DVD-RAMs, DVD-RWs, CD-RWs and the like are known. In such rewritable optical discs, information is rewritten as follows by using laser light. First, an information reproducing apparatus reads out a recording pulse standard condition from a calibration area of an optical disc. Next, the recording and reproducing apparatus irradiates an optical disc with laser light with a waveform which conforms to the recording pulse condition to record information. In order to reduce influence on quality of recording due to variances in optical disc properties and/or recording properties of the recording and reproducing apparatus in such a process, the recording pulse condition to be set has to be optimized. Particularly, when the recording pulse standard condition does not conform to the actual properties of the optical disc, high recording quality has to be secured by optimizing the recording pulse condition.
In a phase change optical disc, heat of the applied laser light forms an amorphous area (mark) and an optical reflectance changes. As a change of the optical reflectance, data is recorded on the optical disc. Particularly, in high-density recording, sizes of a mark to be formed and a space (an area between marks) are small. Thus, the heat of the laser light applied for forming a mark is conducted not only to that mark but also to marks on front and back sides via the spaces. Thus, shapes of the marks may be distorted easily. In order to avoid such distortion, the recording pulse condition is set as follows, for example (see, for example, Japanese Laid-Open Publication Nos. 2000-200418 and 2004-335079). When the laser light is formed of a plurality of pulse train (multipulse), a position of the first pulse varies depending upon a combination of a self-mark length and a length of the front space. On the other hand, a position of the last pulse varies depending upon a combination of the self-mark length and a length of the back space. Such a displacement of the recording pulse compensates for thermal interference between the marks. This type of position control of the recording pulse is generally referred to as recording compensation.
According to a recording method disclosed in Japanese Laid-Open Publication No. 2000-200418, the position of the recording pulse is specified for each of the possible combinations of the mark lengths and the space lengths. The positional information is the recording pulse standard condition. The recording pulse standard condition is read out from the optical disc before recording. Further, the read out recording pulse standard condition is modified, and the recording pulse condition is optimized as follows. First, the positional information related to all the combinations of the mark lengths and the space lengths included in the recording pulse standard condition is used to perform first trial writing to the optical disc. Secondly, the data recorded as a result of the first trial writing is reproduced and a first jitter is detected from a reproduction signal. Thirdly, the positional information related to the all the combinations of the mark lengths and the space lengths included in the recording pulse standard condition is changed uniformly. Fourthly, the uniformly changed positional information is used to perform second trial writing onto the optical disc. Fifthly, the data recorded in the second trial writing was reproduced and a second jitter is detected from the reproduction signal. Sixthly, the first jitter and the second jitter are compared to each other, and the positional information used for the trial writing which generates a smaller jitter is selected as the optimal recording pulse condition.
For optimizing the recording pulse condition, as shown in Japanese Laid-Open Publication No. 2004-335079, for example, a maximum likelihood decoding may be used instead of comparison of jitters. In the maximum likelihood decoding, a pattern which a reproduction signal should have is estimated from an actual waveform of the reproduction signal. Then, the actual waveform of the reproduction signal and the estimated pattern are compared and the most probable pattern is defined. The recording pulse condition is optimized such that a probability that error occurs during decoding becomes the lowest.